Translator fixture with module for expanding test points

ABSTRACT

A translator fixture for a grid-type test fixture for testing circuit boards. In regions of the circuit board where test point density exceeds the grid spacing of probes in a grid base the test points are reached by a test module that plugs into the translator fixture and includes a grid pattern of feed-through probes for contacting special tilt pins connected to certain test points in the high density region of the board. Additional test probes, located between the rows and columns of feed-through probes, support special tilt pins for translating the remaining test points in the high density region of the board to contacts on flex circuit-type cables sandwiched on the module and extending to the periphery of the fixture for coupling to contacts on the grid base to communicate with test circuits in the test analyzer. A translator module providing an interface between the bottom of the translator fixture and the grid base includes a translator board overlying the grid base and translating test signals from a high density set of contacts on one side of the board to a standard pattern of contacts on the other side aligned with the test probes on the grid base. A receiver plate overlying the translator board receives tilt pins with a high density spacing and provides compliant connections to the high density pattern of contacts on the translator board.

CROSS-REFERENCE TO RELATED APPLICATION

This is a division of application Ser. No. 08/593,177 filed Feb. 1,1996, (now U.S. Pat. No. 5,633,598) which is a continuation ofapplication Ser. No. 08/417,441, now abandoned, filed Apr. 5, 1995,which is a continuation of application Ser. No. 08/200,783, filed Feb.23,1994, which is a CIP of 08/081,681 filed Jun. 23,1993, both nowabandoned.

FIELD OF THE INVENTION

This invention relates to the automatic testing of printed circuitboards, and more particularly, to grid fixtures of the type using atranslator fixture for translating test points from an off-grid patternon a board under test to a grid base having test probes on a standardgrid pattern. The invention includes a high density translator modulethat cooperates with the translator fixture for testing high test pointdensities on the board under test, using the lower-density standard gridbase.

BACKGROUND OF THE INVENTION

Automatic test equipment for checking printed circuit boards has longinvolved use of a "bed of nails" test fixture in which the circuit boardis mounted during testing. This test fixture includes a large number ofnail-like spring-loaded test probes arranged to make electrical contactunder spring pressure with designated test points on the circuit boardunder test, also referred to as the unit under test or "UUT." Anyparticular circuit laid out on a printed circuit board is likely to bedifferent from other circuits, and consequently, the bed of nailsarrangement for contacting test points in the board must be customizedfor that particular circuit board. When the circuit to be tested isdesigned, a pattern of test points to be used in checking it isselected, and a corresponding array of test probes is configured in thetest fixture. This typically involves drilling a pattern of holes in aprobe plate to match the customized array of test probes and thenmounting the test probes in the drilled holes on the probe plate. Thecircuit board is then mounted in the fixture superimposed on the arrayof test probes. During testing, the spring-loaded probes are broughtinto spring-pressure contact with the test points on the circuit boardunder test. Electrical test signals are then transferred from the boardto the test probes and then to the exterior of the fixture forcommunication with a high speed electronic test analyzer which detectscontinuity or lack of continuity between various test points in thecircuits on the board.

Various approaches have been used in the past for bringing the testprobes and the circuit board under test into pressure contact fortesting. One class of these fixtures is a "wired test fixture" in whichthe test probes are individually wired to separate interface contactsfor use in transmitting test signals from the probes to the externalelectronically controlled test analyzer. These wired test fixtures areoften referred to as "vacuum test fixtures" since a vacuum is applied tothe interior of the test fixture housing during testing to compress thecircuit board into contact with the test probes. Customized wired testfixtures of similar construction also can be made by using mechanicalmeans other than vacuum to apply the spring force necessary forcompressing the board into contact with the probes during testing.

The wire-wrapping or other connection of test probes, interface pins andtransfer pins for use in a wired test fixture can be time intensive.However, customized wired test fixtures are particularly useful intesting circuit boards with complex arrangements of test points andlow-volume production boards where larger and more complex and expensiveelectronic test analyzers are not practical.

As mentioned previously, the customized wired test fixtures are oneclass of fixtures for transmitting signals from the fixture to theexternal circuit tester. A further class of test fixtures is the socalled "gridtype fixture" in which the test points on the board arecontacted by translator pins which contact random patterns of testpoints on the board and transfer test signals to interface pins arrangedin a grid pattern in a receiver. In these grid-type testers, fixturingis generally less complex and simpler than in the customized wired testfixtures; but with a grid system, the grid interfaces and testelectronics are substantially more complex and costly. It is thegrid-type testers to which the present invention is directed.

A typical grid fixture contains test electronics with a huge number ofswitches connecting test probes in a grid base to corresponding testcircuits in the electronic test analyzer. In one embodiment of a gridtester as many as 40,000 switches are used. When testing a bare board onsuch a tester, a translator fixture supports translator pins thatcommunicate from a grid pattern of test probes in a grid base to anoff-grid pattern of test points on the board under test. In one priorart grid fixture so-called "tilt pins" are used as the translator pins.The tilt pins are mounted in corresponding pre-drilled holes intranslator plates which are part of the translator fixture. The tiltpins can tilt in various orientations to translate separate test signalsfrom the off-grid random pattern of test points on the board to the gridpattern of test probes in the grid base. This grid pattern of testprobes in the grid base communicates with the test electronics throughthe respective switches previously mentioned. In a typical grid-typetest fixture the grid base may have its test probes arranged on 100 milcenters. The tilt pins used in the translator module make contact with apreselected number of test points on the board and then make contactwith selected test probes in grid base, and as a result, a large numberof switches which are connected to all of the probes in the grid base gounused during testing, which is a typical characteristic of grid-typetest fixtures. Because the spacing density among test probes in the gridbase is limited, test points on a board having a density greater thanthe typical 100 mil on-center grid base density, for example, cannot beeasily tested on the standard 100 mil center grid-type fixture. For bareboards today which have closer and closer test point densities, itbecomes extremely more difficult to test these boards on the standardgrid-type test fixture.

One embodiment of the present invention provides a fixturing system forselectively modifying the test point density of a grid-type test fixtureto provide accurate testing for greater test point densities than wouldotherwise be available with a standard translator fixture and thestandard grid pattern. The invention includes an adapter that cooperateswith the translator fixture to expand test point densities for boards orportions of boards having test points arranged in high density patterns,substantially higher than the density of the probes in the standard gridbase. The adapter allows use of tilt pins to translate test signals fromhigh density test points on the board under test to the lower densitygrid pattern of test points in the standard grid base.

SUMMARY OF THE INVENTION

Briefly, one embodiment of the invention provides improvements to agrid-type test fixture system for testing printed circuit boards. Thesystem includes a grid base supporting test probes arranged on a gridpattern. The probes in the grid base are individually connected tocorresponding electrical test circuits in an external automaticelectronic test analyzer. A translator fixture is mounted on the gridpattern of probes in the grid base and supports the board under test.The translator fixture has vertically spaced-apart and parallelfixturing plates with holes drilled in patterns to support individualupright translator pins, such as tilt pins, for translating electricalconnections between an off-grid pattern of test points on the board tothe grid pattern of corresponding probes in the grid base. In certainregions of the board where the test point density exceeds the standardon-center spacing of the probes in the grid base, the test points arereached by a high density plug-in test module that locally expands thenumber of test points for a given area. The high density test modulefits into a cutout space in a bottom plate of the translator fixture andincludes a grid pattern of feed-through probes for contacting specialtilt pins connected to certain test points in the high density region ofthe board. The feed-through probes in the module make normal springcontact with the grid pattern of probes in the grid base. The highdensity test module also includes an array of additional test probeslocated between the rows and columns of feed-through probes. Theadditional probes support further corresponding special tilt pins forcompleting contact with test points in the high density region of theboard. The additional test probes make contact with electrical terminalsof circuits contained on one or more flexible sheet-like flex cablescarried on the high density translator module. The flex circuit cablesextend to the periphery of the test fixture for coupling to the gridbase and ultimately to the test circuit electronics in the electronictest analyzer. These connections are made without the need forincreasing the number of electronically controlled test circuits in thetester.

This embodiment of the invention can be used with an otherwise standardgrid-type tester to greatly increase the density of test points inselected regions of the board under test, over and above the test pointdensity normally available from the on-grid pattern of probes on thestandard grid base. This testing is accomplished with existingelectronic circuitry normally available in the standard high speedelectronic test analyzer.

In another form of the invention, a grid-type test fixture for testing aprinted circuit board includes a grid base supporting spring-loaded testprobes arranged in a grid pattern having a standard on-center spacing inwhich the probes in the grid base are individually connected tocorresponding test circuits in an exterior automatic electronic testanalyzer. A translator fixture for supporting the board under test ismounted between the grid base and the board. The translator fixturesupports translator pins for translating electrical connections from anoff-grid pattern of test points in the board to the grid pattern ofspring probes in the grid base. The invention comprises a translatormodule for use in testing circuits on the board having test pointdensities greater than the standard on-center density of test probes inthe grid base. The translator module includes a translator board havinga first pattern of electrically isolated and electrically conductivecontacts on a first side of the board communicating electrically with asecond pattern of electrically isolated and electrically conductivecontacts on a second side of the translator board. The spacing betweencontacts on the first side of the board is at a higher density than thespacing between contacts on the second side of the board. In use, thetranslator board is mounted over the grid base to align the contacts onthe second side of the board with corresponding spring probes on thegrid base. The translator module also includes a translator pin receiverplate mounted above the first surface of the translator board and belowthe translator fixture. The receiver plate has a first surface facingtoward the translator fixture for containing a pattern of electricallyisolated receiver holes on a pattern aligned with the higher densityfirst pattern of contacts on the translator board. The receiver holesare adapted to receive the ends of separate translator pins supported bythe translator fixture. Compliant electrical contact means within eachreceiver hole engage corresponding translator pins and produce compliantelectrical contact between the translator pins and the higher densityfirst pattern of electrical contacts on the translator board alignedwith the corresponding receiver holes. When a compliant force is appliedduring testing, test signals are translated from the board under testthrough the translator pins to the compliant connections provided by thereceiver plate and are then translated through the translator board tothe test probes on the grid base.

This invention is particularly useful in testing small credit card sizedcircuit boards having test points on high density test patterns. Theinvention is carried out by mounting the translator module between thestandard translator fixture and the standard grid base. The translatorpins communicate with the high density test points on the board and themodule then translates the test signals carried by its high densitytranslator pins to the standard on-grid pattern of test probes on thegrid base, while simultaneously providing the compliancy necessary fortranslating reliable test connections from the high density off-gridpattern to the lower density standard grid spacing of test probes on thegrid base.

A further advantage of the invention is that the receiver plate andtranslator plate can be mounted in a combination that universallyaccepts the same translator fixture which can have various arrangementsof translator pin configurations. The translator fixture and theconnections from the fixture and from the translator module to the gridbase need not be modified for each different board being tested.

In another embodiment of the invention, a uniform pressure transmittingsystem maintains uniform pressure on the board under test and on thetranslator module when compliant pressure is applied to the entire testassembly during testing. The pressure transmitting system includes arigid frame mounted around the peripheries of the translator fixture andthe translator module to spread the forces applied during testing toprevent undue bending forces being applied to the board under test or tothe translator module.

These and other aspects of the invention will be more fully understoodby referring to the following detailed description and the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram illustrating components of atranslator fixture and a high density test point expansion module forexpanding test points according to principles of this invention.

FIG. 2 is a semi-schematic cross-sectional view illustrating thetranslator fixture without the module.

FIG. 3 is a semi-schematic cross-sectional view similar to FIG. 2 butshowing the test module in use.

FIG. 4 is a semi-schematic perspective view illustrating the test moduleand flex cables.

FIG. 5 is a schematic plan view illustrating a configuration offeed-through holes and additional electrical connections to circuitsprinted on a flex cable sheet contained in the expansion module.

FIGS. 6 and 7 are similar semi-schematic cross-sectional viewsillustrating the test module in use during an uncompressed andcompressed state, respectively.

FIG. 8 is an exploded perspective view showing components of analternative form of the invention comprising a translator module and aforce absorbing outer frame for use in simultaneously testing multiplecircuit boards each having test points in patterns of higher densitythan the grid pattern of test probes on a standard grid base.

FIG. 9 is a top elevational view taken on line 9--9 of FIG. 8.

FIG. 10 is a bottom elevational view taken on line 10--10 of FIG. 8.

FIG. 11 is a fragmentary schematic cross-sectional view illustratingcomponents of a translator module according to the alternativeembodiment of the invention.

FIG. 12 is a schematic cross-sectional view showing the translatormodule of FIG. 11 in use between a translator fixture and a standardgrid base.

FIG. 13 is a perspective view showing the components of FIG. 8 duringuse.

DETAILED DESCRIPTION

Referring to the schematic block diagram of FIG. 1, a grid-type printedcircuit board tester includes a grid base 10 having an array ofspring-loaded test probes 12 arranged on a two-dimensional grid pattern.The uniform array of probes preferably comprises an orthogonal array ofuniformly spaced-apart rows and columns of test probes which may bealigned on 100 mil centers as an example. A translator fixture 14supports a printed circuit board 16 under test. The translator fixtureserves as an interface between an array of test points 18 and 18' on theboard under test and the test probes 12 in the grid base 10. An externalelectronic test analyzer 20 is electrically connected to the test pointsin the board through test probes in the translator fixture. These testprobes (of which there are several types) are illustrated generally at22 and 24 in FIG. 1 and will be described in more detail below.

The test analyzer 20 contains electronic interrogation circuits toelectronically interrogate the separate test points 18 and 18' of theboard under test in order to determine whether or not an electricalconnection exists between any two given test points. The electricalconnections detected between test points on the tested board areelectronically compared with stored reference results obtained from aprevious interrogation of test points of a faultless master printedcircuit board. The tested board is good if test results match the storedreference results, but if any problem exists in the circuits on theboard, the problem is detected by the test results and the bad boardsthen can be separated from the good boards.

The electronic interrogation circuits, in one embodiment, comprise aplurality of printed circuit cards (sometimes called "switch cards")having electronic components and printed circuits for carrying outelectronic testing. Each test probe used in the test procedure isrepresented as being coupled to the test electronics through acorresponding switch 26 leading to the test analyzer. In a givengrid-type tester there can be as many as 40,000 switches available fortesting the various test points in a board under test. However, as istypical with a grid-type fixture, many of these switches and the relatedelectronic test circuitry goes unused when testing a given board, whileonly a selected percentage of test circuits having connections with thetranslator fixture 14 are actually used. As mentioned, the translatorfixture provides the interface between the test points 18 and 18' beingtested and the circuits within the electronic test analyzer 20 which areused to carry out the test.

The invention is useful for locally expanding the density of test pointsin regions within the fixture matching regions within the board undertest where test point density exceeds the standard on-center density ofgrid base test probes 12. For instance, in a tester in which the arrayof grid base test probes has an on-center spacing of 100 mils, there maybe regions within the board under test where spacing between test points18' is between say 50 and 100 mils. (Test points 18 are represented asareas of the board where the density of test points generally does notexceed a level that can be normally reached by test probes connected tothe standard grid base probes. Test points 18' represent areas of theboard where test point density is much greater and cannot be reached bytest probes connected to the standard grid base.) The high densityspacings may be spread out in two dimensions across the board in arandom pattern of closely spaced test points 18'. For these localizedhigh density test point regions, the invention provides a means forfixturing high density patterns of test probes to translate test signalsfrom the high density test points 18' on the board to the test circuitswithin the test analyzer 20. Many of the test circuits to which the testpoints 18' are connected by the translator fixture are test circuitswhich are otherwise unused by the normal grid pattern of test probes.

The translator fixture 14 shown in FIG. 2 includes a series ofvertically spaced-apart and parallel fixturing plates which include atop plate 28, an upper plate 30 spaced a short distance below the topplate, a lower plate 32 at approximately an intermediate level of thetranslator fixture, and a pair of base plates 34 and 36 which are partof a sandwich-type retainer assembly that also includes a pin retainer38 sheet of flexible plastic sandwiched between the bottom plates 34 and36.

The fixture includes an array of standard translator pins such as tiltpins 40 extending through the fixturing plates 28, 30 and 32 and throughthe base plate retainer assembly 34, 36, 38. FIG. 2 shows only a pair ofstandard tilt pins 40 for simplicity. The tilt pins extending throughthe base plate retainer assembly are in alignment with the grid patternof probes 12 in the grid base 10. The top portions of the tilt pins,which extend through the top plate 28, are in an off-grid patternaligned to match the random pattern of test points on the UUT. Thus, thetilt pins can be tilted slightly and various three dimensionalorientations in order to translate between the grid pattern at the baseto the off-grid pattern at the top. The standard tilt pins pass throughholes 42 in the lower plate 32, through holes 44 in the upper plate 30,and through a hole pattern 45 in the top plate 28. The bottoms of thepins 40 are retained in holes 46 in the base plate retainer assembly.The plastic sheet 38 of the retainer assembly has undersized holes thatgrip the probes 40 to provide the retention. Standard computer operatedsoftware is used for controlling drilling of the hole patterns in thefixturing plates according to wellknown procedures for aligning the tiltpins in the various orientations to translate from the grid pattern atthe base to the off-grid pattern at the top.

For those regions of the UUT where test points 18' are in densitiesgreater than the standard density of oncenter spacing of the probes 12in the grid base 10, the invention provides a high density test pointexpansion module 47 (described in greater detail below) for aligningtilt pins in the closer spacings necessary to match the high densitypatterns of test points 18' on the UUT. Each high density test pointexpansion module is mounted in a corresponding cutout space 48 formed inthe base plate retainer assembly of the translator fixture. A pluralityof such cutout spaces can be formed throughout the translator fixturefor alignment with any corresponding pattern of high density test pointsin the UCT. Only one is shown in FIG. 2 for simplicity. The cutoutspaces are preferably milled in the base plate retainer assembly in anydesired pattern, but the embodiments shown in the drawings illustrate arectangularly shaped cutout for receiving a module of similarrectangular shape. In those regions of the translator fixture where thecutout spaces 48 are formed to receive a test point expansion module 47,special tilt pins 50 are used for translating test signals between theUUT and connections within the translator module. As will be describedin more detail below, the density of special tilt pins 50 greatlyexceeds the normal density of standard tilt pins 40. Only one suchspecial tilt pin 50 is shown in FIG. 2 for simplicity. In areas wherethe special tilt pins 50 are mounted above the cutout space 48 for thetest point expansion module, a secondary retainer assembly 52 isattached to the lower plate 32 in a sandwich structure which alsoincludes a plastic retainer sheet 54 between the retainer plate 52 andthe lower plate 32. The retainer assembly 52, 54 retains the specialtilt pins 50 in alignment with corresponding connections in the testpoint expansion module while the tilt pins 50 extend upwardly through apattern of drilled holes 56 in the upper plate and through acorresponding pattern of drilled holes 57 in the top plate 28. The holepattern 57 is in alignment with the high density pattern of test points18' on the UUT 16. (The retainer assembly 52, 54 for the special tiltpins 50 is one of several possible arrangements; an alternativeembodiment is shown in FIG. 3.)

FIG. 3 is a schematic cross-sectional view showing the high density testpoint expansion module 47 positioned within the cutout space 48 in thebase plate 34 of the fixturing assembly. The module comprises anelectrically insulating housing with holes drilled through it in anarray that combines a first two dimensional pattern of spaced-apartfeed-through holes 58 matching the grid pattern of probes 12 in thestandard grid base 10, together with an intervening second array ofspaced-apart holes 59 in spaces between the first grid pattern of holes.The holes in each group mount corresponding electrical contacts such asspring probes for contact with the special tilt pins 50. The specialtilt pins are retained in holes 55 in a secondary retainer assembly 32,52, 54 attached below a cutout opening 48' in the lower fixturing plate32. The cutout opening 48' provides for vertical positioning of the testpoint expansion module 47. The secondary intervening hole pattern 59provides spaces within the module for mounting the additional springprobes 50 to accommodate the additional test points within the highdensity region of the test points 18' on the board under test. Thecross-sectional view of FIG. 3 illustrates a row of holes drilled in themodule housing which includes holes from both groups of hole patterns.The illustrated row of holes includes the spaced-apart holes 58 alignedwith the grid pattern of spring probes 12 in the grid base 10 and theadditional holes 59 located in the intervening spaces between adjacentpairs of standard grid pattern holes 58. Spring probes 60 are mounted inthe standard grid pattern of holes 58 in the module with fixed pins 61from the base of the probes 60 projecting from the bottom of the modulehousing. Thus, a two-dimensional grid pattern of pins 61 projects fromthe bottom of the housing for alignment with the corresponding gridpattern of probes 12 in the grid base 10. The array of additional holes59 extending through the module housing support spring probes 62 whichare seated in lower portions of the holes 59. These probes have shortfixed pins 64 at their base which are soldered or otherwise electricallyconnected to corresponding circuit traces 66 (see FIG. 4) on a flexiblesheet-like flex cable film 68 laminated to a lower portion of the modulehousing. End portions of the flex cable film extend outwardly from themodule. The ends of the flex cables include plug-type connectors 70 formaking electrical connections to electrical circuits within the externalautomatic circuit test analyzer 40. These circuits are coupled tocorresponding switch cards within the test analyzer that are otherwisebeing unused by the fixturing connections to the test probes 12 of thestandard grid probe plate.

When mounting the test point expansion module 47 within the cutout space48 in the lower portion of the fixture, the module is aligned above andsecured to a lower stripper plate 72 having an array of holes 74matching the grid pattern of probes 12 in the grid base.

FIG. 4 illustrates one embodiment of the module housing in which thereare four flex cables 68 extending from the four sides of the module forconducting test signals from the high density probes 62 to the externalcircuit tester. As shown in FIG. 5, each flex circuit cable canterminate in an angled quadrant of the module housing and then extend tothe exterior from each of the four sides of the housing. Alternatively,the flex cables can be limited to extending from only two sides of themodule, say from opposite sides, by joining together two of the flexcables on each side of the module. In the latter case, the two joinedcables attach to the module at different levels for connection to thepins 64.

FIG. 5 illustrates a typical arrangement of printed circuits on the flexcable that are aligned with and in communication with the sets of gridpattern holes and their probes, together with the high density set ofholes and their corresponding probes. As illustrated in FIG. 4, theon-grid pattern of probes 60 provide feed-through connections at thelevel of the flex circuit within the housing; the intervening highdensity probes 62 are each connected to corresponding printed circuitson the flex circuit film for extending test signals to the external testanalyzer away from and independently of the grid base probes 12. Theprobes 60 extend through the flex circuit film within the module withoutmaking electrical contact with the circuits on the flexible plasticfilm.

In use, the test point expansion module 47 is plugged into thepre-drilled hole 48 within the base of the translator fixture 14 inregions of high density test probing, and the external flex circuitcable connectors 68 that extend away from each module are preferablytwisted 90 degrees so that they can be fed through the field of tiltpins for extending to the exterior of the fixture for connection to thetest analyzer. The ends of the flex cables have corresponding connectorsthat releasably engage the spring probes in the grid base around theperiphery of the translator fixture. The short special translator pinsor tilt pins 50 are used for connection to both sets of feedthrough testprobes 60 and high density expansion probes 62 within the module.

FIGS. 6 and 7 illustrate the translator module positioned within thetranslator fixture in which the test system shown in FIG. 6 is in anuncompressed state, and the system of FIG. 7 is shown in its compressedstate with the translator fixture having moved down toward the gridbase.

Thus, the invention provides a means for expanding the density ofmultiple test points in an area or areas within a translator fixturewithout adding external electronics to the fixturing system in order totest high density regions of the board under test. As a result, the samehigh speed electronic test analyzer can be used with the same standardgrid base, with the test points in the high density regions being tiedto areas within the test analyzer which are not otherwise being used. Asa result, printed circuit boards having extremely small spacingdistances for smaller and smaller sizes of integrated circuits and thelike can be tested on the otherwise standard grid-type test fixtures.

FIGS. 8 through 13 illustrate an alternative embodiment of the inventionwhich is useful for testing bare boards with high density randompatterns of test points, in which the board is tested on a grid-typetester having a grid base with a standard on-center spacing of testprobes, and in which the spacing among test points on the board undertest is much greater than the spacing between spring probes in the gridbase. The invention is particularly useful in testing small credit cardsized circuit boards having high density patterns of test points. Forinstance, the board under test can have test points spaced apart by lessthan 50 mils whereas the on-center spacing between test probes in thestandard grid base can be 100 mils. This arrangement can require tiltpins in the translator fixture to reach too far in making contactbetween the dense pattern of test points and the probes in the standardgrid base. Use of tilt pins in this instance also can produce errors inthe test results.

In the past, one approach to avoiding this problem when testing theseboards on a grid fixture is to divide the tests into two phases: one fortesting power and ground connections, and the other for functionaltesting. However, this requires configuring the translator fixture andits tilt pins twice, once for each test.

The present invention overcomes these problems by providing a translatormodule that can be used with the standard translator fixture and thestandard grid base, to translate high density patterns of test points inmultiple small circuit boards tested simultaneously in a single test. Asa result, the loss of time in reconfiguring the translator fixture isavoided and testing is also sped up because multiple circuit boards canbe tested at once. Further, the invention has the advantage that thetranslator module can be used interchangeably with different translatorfixtures adapted for testing different circuit boards without makingmodifications to the system software, inasmuch as the same test probeson the grid base can be used for each different test fixture.

These advantages will be more fully apparent by referring to thefollowing description as it relates to the embodiment of FIGS. 8 through13.

The exploded perspective view of FIG. 8 illustrates components of thesystem for simultaneously testing a plurality of small credit card sizedcircuit boards 80 having high density patterns of test points 82 (shownbest in FIG. 12). The assembly includes a translator module 84positioned between the grid base 10 and a translator fixture 86. Thetranslator module includes a translator board 88 that rests on the gridbase and a test pin receiver plate 90 supported on top of the translatorboard and adapted to receive the bottoms of tilt pins (see FIGS. 11 and12) contained in the translator fixture. The translator fixture includesa plurality of vertically spaced-apart, horizontally positioned andparallel translator plates with holes drilled in a hole pattern thatsupports the tilt pins in a manner similar to that described for theembodiment of FIGS. 1 to 7. In the present embodiment the translatorfixture includes a rectangular top plate 94 of enlarged surface areacompared to the other translator plates in the fixture. The fixture alsoincludes an upper translator plate 96 and a lower translator plate 98.The translator plates are best shown in FIG. 12 which also showsvertical stand off posts 100 spaced apart around the periphery of thefixture for securing the translator plates of the fixture together as arigid unit.

The assembly of FIG. 8 also includes a rigid pressure-absorbing outerframe 102 having upright column-like pressure feet 104 supported on andspaced apart around the periphery of a rectangular peripheral plate 106.A rectangular cutout 108 centrally disposed in the rectangularperipheral plate 106 matches the shape of the rectangular pin receivingplate 90 of the translator module which extends into the space withinthe cutout during assembly.

FIGS. 9 through 11 illustrate detailed construction of the translatorboard 88. The board includes a multi-layer circuit board made from anelectrically insulating material and having parallel first and secondsurfaces 110 and 112. A first array of electrically conductive pads 114faces upwardly from the first surface of the board, and a second arrayof electrically conductive pads 116 faces down from the second surfaceof the board. The first array of test pads are spaced closer together inrows and columns to form a high density array of pads facing upwardlyfrom the board. The second array of pads are spread apart in rows andcolumns of wider spacing than the pads on the other side of the board.The same number of pads are used on both sides of the board, and eachpad on one side is electrically connected internally to a correspondingpad on the other side. The internal connections are translated betweenpads in the same locations in the arrays on both sides so thatelectrical contact with a given pad on one side can be easily identifiedwith a corresponding pad at the same location in the array on theopposite side. In one embodiment, the translator board has eightthousand pads on each side and the spacing between pads 114 on the firstside of the board is 5 mils and the spacing between the pads 116 on thesecond side of the board is 10 mils, both being in uniform grid patterns(parallel rows and columns uniformly spaced apart by the same distance).

The 10 mil spacing between the test pads 116 on the second side of thetranslator board is adapted for alignment with a corresponding 10 milspacing of the grid pattern of spring-loaded test probes 12 in the gridbase 10, as shown best in FIG. 12. The 10 mil spacing is described asone embodiment. If a grid base of a gridtype fixture contains springprobes arranged on a grid pattern having a different spacing, thespacing among test pads 116 on the bottom of the translator board isarranged accordingly in order to match the pattern of spring probes inthe grid base.

Referring to FIG. 11, the translator module 84 also includes thetranslator pin receiving plate 90, which may also be referred to as acassette. Although the pin receiving plate is shown in FIGS. 8 and 13 asa two layer board, the board is also shown as a single layer board forsimplicity in FIGS. 11 and 12. The receiving plate includes a rigidplate made from an electrically insulating material and having an arrayof compliant electrical translator means within the plate arranged on apattern corresponding to the pattern of test pads 114 on the firstsurface of the translator board to which the plate is mounted. In theillustrated embodiment, the compliant translator means comprise separatetranslator pin receiver holes 118 arranged in an array on a top face 120of the receiver plate. The pin receiver holes are adapted to receive andretain the bottom end portions of the translator pins 92 carried by thetranslator fixture. The lower portions of the receiving holes areenlarged to contain separate spring biased electrical contacts 122 whichare movable within the receiver plate and biased by correspondingcompression springs 124. When the receiver holes and their correspondingcompliant spring contacts 122 are aligned with the test pads 114 on thetranslator board, electrical contact is completed from the bottoms ofthe tilt pins 92, through the spring contacts 122, through theconductive springs 124, to the test pads 114 on the translator board.

The pin receiving plate also includes a plurality of spring-biasednon-conductive pressure-distributing buttons 126 spaced apart around theperiphery of the plate. The buttons are spring-biased to normallyproject above the upper surface of the plate by separate captivecompression springs 128.

FIG. 12 illustrates use of the translator system in which anelectrically conductive stripper plate 130 is first positioned over thespring probes 12 of the grid base 12. The spring probes 10 project intocorresponding transfer holes 132 drilled on a corresponding grid patternin the stripper plate. To accommodate vertical travel during use, thestripper plate can include a rectangular recessed region 134 forreceiving the translator module to align the spring probes for contactwith the pads at the bottom of the translator board. Tooling pins intooling pin holes of the translator board provide the alignment. Whenthe translator module is aligned in the stripper plate, the contactbetween the spring probes of the grid base is translated through thealigned test pads 116 internally through the translator board to thetest pads 114 on top of the board. These test pads communicate with thespring contacts 122 in the translator pin receiver holes 118 of thereceiver plate 90. When the translator fixture is positioned above thetranslator module, the fixture rests on the spring-biased bottom 126 toinitially align the fixture parallel to the translator module and thegrid base. The buttons initially support the fixture spaced parallelabove the translator module. The bottoms of the tilt pins 92 are alignedwith corresponding receiver holes 118 in the receiver plate 90. Thetranslator fixture is positioned above the top surface of the translatorpin receiver plate so the tilt pins supported by the translator fixturecan move into the corresponding pin receiver holes 118 when a downwardcompression force is applied during testing. The circuit board undertest 80 is positioned on top of the translator fixture and the tilt pins92 being positioned to correspond to the pattern of test points on theunderside of the board 80 provides electrical test signal communicationfrom the underside of the board to the spring contacts 122 in thetranslator pin receiver holes 120. Thus, a high density pattern of testpoints 82 on the board under test is translated to a high densitypattern of spring contacts contained within the upper portion of thetranslator module, the difference being that the tilt pins translate thehigh density random off-grid pattern of test points to an on-gridpattern. The translator fixture is positioned so that the stand-offposts 100 of the fixture are aligned vertically and positioned on top ofthe spring-loaded buttons 126 that are spaced apart around the peripheryof the translator pin receiving plate 90. Thus, each spring-loadedbutton 126 is aligned with a corresponding post 100 of the translatorfixture. In addition, spacers 140 are positioned around the periphery ofthe top plate 94 of the translator fixture to surround the circuit board80 under test. The spacers 140 have the same thickness as the circuitboard 80 under test. These spacers are also aligned vertically with theposts 100 of the translator fixture and the pressure buttons 126 on thetranslator module.

The outer pressure distributing frame 102 is placed around the outsideof the translator module and the translator fixture. As shown best inFIG. 12 the bottom of the peripheral frame 106 rests on the peripheraltop face of the translator board 88 which surrounds the translator pinreceiving plate 90. With the pressure distributing frame 102 arrangedaround the periphery of the translator module, the pressure distributingposts 104 are also spaced around the outside of the translator modulewith their top surfaces spaced a short distance of travel from theunderside of the translator fixture's top plate 94 (as shown best inFIG. 12). The translator fixture further includes spacers 142 having athickness the same as the board 80 under test arranged around theperiphery of the top plate 94 of the test fixture.

During use, a force-applying platen 150 on the exterior of the testerapplies a downward force to the translator fixture to compress theprobes within the fixture to produce compliant mechanical and electricalcontact necessary to produce reliable electrical connections from theboard under test, through the tilt pins to the compliant contacts in thetranslator module, and through the translator board to the spring probesin the grid base. Pressing down on the top of the board under test canhave a tendency to bend the periphery of the board so it bows upwardly,but the spacers 140 and 142 of the same thickness as the board undertest prevent the board from bending. The downward compression forces aretranslated through the stand-off posts 100 in the translator fixture tocompress the compliant buttons 126 at the periphery of the receiverplate on the translator module. The downward pressure then causes thebottoms of the tilt pins to move into the receiver holes and compressthe spring-biased contacts 122 in the receiver plate as the bottom ofthe translator fixture moves onto the receiver plate. This downwardforce can have a tendency to cause the periphery of the translator boardto bow upwardly, but the rigid pressure-absorbing frame 106 mountedaround the top peripheral portion of the translator board resistsbending of the board. The column-like force-absorbing feet 104 arespaced apart around the periphery and a downward force of the platendirected onto the columns spreads the force to compress the translatorboard uniformly.

What is claimed is:
 1. In a grid-type test fixture for testing a printedcircuit board in which the grid fixture includes a grid base supportingspring-loaded probes arranged in a grid pattern having an on-centerspacing, the probes in the grid base being individually connected tocorresponding electrical test circuits in an external automaticelectronic test analyzer, and a translator fixture supporting thePrinted circuit board and mounted between the grid base and the Printedcircuit board, the translator fixture having vertically spaced-aparttranslator plates with holes drilled in patterns to support individualtranslator pins inserted into the holes of the translator plates fortranslating electrical connections between an off-grid pattern of testpoints in the printed circuit board to the grid pattern of correspondingspring probes in the grid base, the improvement comprising a translatormodule for use in testing circuits in a high density region on theprinted circuit board having test point densities greater than thestandard on-center density of the spring-loaded probes in the grid base,the translator module comprising a circuit translating board havingparallel first and second sides, the first side having a first patternof separate electrically isolated and electrically conductive contacts,the second side having a second pattern of separate electricallyisolated and electrically conductive contacts, the first pattern ofcontacts having a higher density than the second pattern, the secondpattern of contacts matching the pattern of the spring-loaded probes onthe grid base, the circuit translating board mounted on the grid base toalign the second contacts thereon for electrical contact with the springprobes on the grid base, the translator module further including atranslator pin receiver plate mounted above the first surface of thecircuit translator board and below the translator fixture, the| receiverplate having parallel first and second faces, the first face thereoffacing toward the translator fixture and containing a pattern ofelectrically isolated receiver holes on a pattern aligned with the highdensity first pattern of contacts on the circuit translating boardmounted below the receiver plate, the receiver holes adapted to receivethe ends of separate translator test pins supported by the translatorfixture which are inserted into the receiver holes for communicatingbetween test points on the printed circuit board and the receiver holesin the translator pin receiver plate, and compliant electrical contactmeans within each receiver hole to produce compliant electrical contactbetween the inserted translator pins supported by the translator fixtureand the high density first pattern of electrical contacts on the circuittranslator board, wherein electrical test signals pass from the testpoints on the printed circuit board, through the translator pins, and tothe test probes on the grid base via the circuit translating board. 2.The improvement according to claim 1 including a pressure-absorbingframe disposed around the periphery of the translator fixture and thetranslator module for avoiding bending of the translator board under acompression force applied to the board under test.
 3. A grid-type testfixturing system for testing a printed circuit board having a highdensity pattern of test points, the fixturing system comprising:a gridbase supporting spring-loaded test probes arranged in a grid patternhaving an on-center spacing, the probes in the grid base beingindividually connected to corresponding electrical test circuits in anexternal automatic electronic test analyzer, a translator fixturesupporting the board under test and mounted between the grid base andthe board under test, the translator fixture having verticallyspaced-apart translator plates with holes drilled in patterns to supportindividual translator pins separately inserted into the holes of thetranslator plates for translating electrical connections between anoff-grid pattern of test points in the board under test to the gridpattern of corresponding spring probes in the grid base, a translatormodule for use in testing circuits on the board having test pointdensities greater than the standard on-center density of thespring-loaded test probes in the grid base, the translator moduleincluding a circuit translator board having parallel first and secondsides, the first side having a first pattern of separate electricallyisolated and electrically conductive contacts, the second side having asecond pattern of separate electrically isolated and electricallyconductive contacts, the first pattern having a higher density ofcontacts than the second pattern, the second pattern of contactsmatching the standard pattern of the spring-loaded test probes in thegrid base, the circuit translator board being mounted on the grid baseto align the second contacts thereon for electrical contact withcorresponding spring probes on the grid base, the translator modulefurther including a translator pin receiver plate mounted above thefirst surface of the circuit translator board and below the translatorfixture, the receiver plate having parallel first and second faces, thefirst face thereof facing toward the translator fixture and containing apattern of electrically isolated receiver holes on a pattern alignedwith the higher density first pattern of contacts on the circuittranslator board mounted below the receiver plate, the receiver holesadapted to receive the ends of separate translator test pins supportedby the translator fixture and which are separately inserted into thereceiver holes for communicating between a test point on the board undertest and the receiver holes in the translator pin receiver plate, andcompliant electrical contact means within each receiver hole to producecompliant electrical contact between the translator pins supported bythe translator fixture and the high density pattern of electricalcontacts on the translator board, wherein electrical test signals passfrom test points on the board, through the translator pins, and to thetest probes on the grid base via the circuit translator board. 4.Apparatus according to claim 3 including a rigid force absorbing framedisposed on a peripheral portion of the translator board surrounding thereceiver plate and the translator fixture, the frame includingspaced-apart upright pressure-distributing columns for spreading thecompression force applied to the fixture during testing to preventbending of the translator board and the board under test.
 5. A testfixture for testing a board under test having a random pattern of testpoints, the test fixture comprising:a grid base having spring probesarranged in a uniform array, the board under test having at least aportion of its test points in an array with a density greater than thedensity of the spring probes in the grid base, a translator fixturehaving spaced-apart translator plates with hole patterns in them forsupporting translator pins separately inserted into the holes of thetranslator plates to contact the test points in the board under test,including the high density array of test points, a translator modulepositionable relative to the translator fixture for mounting below atleast a portion of the translator fixture, the translator moduleincluding receiver holes in a first pattern to receive bottom portionsof the translator pins which are inserted into the holes of thetranslator plates for contacting the high density array of test pointsin the board under test, compliant contact means in the receiver holesfor making mechanical and electrical spring-biased contact with thetranslator pins under a force applied during testing of a board undertest, and means for translating test signals from the compliant contactmeans to the spring probes in the grid base independently of andremotely from the translator fixture for translating the test signalscarried by the translator pins from the high density array of testpoints to spring probes within the array of spring probes on the gridbase.
 6. Apparatus according to claim 5 including a rigid forceabsorbing frame disposed on a peripheral portion of a translator boardsurrounding a receiver plate and the translator fixture, the frameincluding spaced-apart upright pressure-distributing columns forspreading the compression force applied to the fixture during testing toprevent bending of the translator board and the board under test.